The present invention relates to a humidifier, a fuel cell system utilizing the same and a humidification process, and particularly to a humidifier utilizing a hollow fiber membrane, a fuel cell system utilizing the same and a humidification process.
Fuel cell systems, especially solid polymer fuel cell systems are widely known as a power source for electric vehicles. In such fuel cell systems, a humidifier is used to moisture-exchange off gas, viz. moist gas discharged from a fuel cell, between its moisture and air as a dry gas, and to generate humidified air or humidified gas. Preferably, a humidifier used with such fuel cell systems is of a lower power consumption type, and is required compactness with less attachment space. For this reason, among many other humidifiers, such as a supersonic humidifier, a steam humidifier, a vaporizing humidifier and a nozzle injection type humidifier, a humidifier utilizing water permeable membranes, especially hollow fiber membranes is commonly used with a fuel cell.
A conventional humidifier utilizing hollow fiber membranes is disclosed in Japanese Laid-open Patent Publication No. HEI-7-71795. As shown in FIG. 23, a humidifier 300 comprises a housing 301, on which is provided a first inlet 302 for introducing dry air and a first outlet 303 for discharging the dry air (humidified dry air). A bundle of hollow fiber membranes 304 consisting of a number of for example 5000 hollow fiber membranes is accommodated within the housing 301.
At both ends of the housing 301, fastening members 305, 305xe2x80x2 are provided for fixing the ends of the bundle 304 while leaving them open. Outside of the fastening member 305 is provided a second inlet 306 for introducing moist air or moist gas, and a second outlet 307 is provided outside of the fastening member 305xe2x80x2 for discharging the moist air, moisture of which is separated and removed at the bundle of hollow fiber membranes 304. The fastening members 305, 305xe2x80x2 are covered with a first head cover 308 and a second head cover 309, respectively. And the second inlet 306 is formed on the first head cover 308, while the second outlet 307 is formed on the second head cover 309.
In the aforementioned humidifier 300 utilizing hollow fiber membranes, the moist air introduced from the second inlet 306 passes through the hollow fiber membranes forming the bundle of hollow fiber membranes 304, and the moisture within the moist air is separated by capillary action of the hollow fiber membranes. The separated moisture moves outward of the hollow fiber membrane through a capillary tube of the membrane. The moisture-removed air is discharged from the second outlet 307.
Meanwhile, dry air is supplied from the first inlet 302. The dry air from the first inlet 302 flows outside of the hollow fiber membranes forming the bundle of hollow fiber membranes. Because the moisture separated from the moist air has moved outside of the hollow fiber membranes, the moisture humidifies the dry air. The humidified dry air is then discharged from the first outlet 303.
However, in the conventional humidifier 300 shown in FIG. 23, the first air inlet 302 which introduces the dry air is formed on the housing 301 at the side near the center of the lengthwise direction thereof. For this reason, as shown in the black arrow of FIG. 23, the dry air flowing outside of the hollow fiber membranes in the bundle 304 of the hollow fiber membrane stored within the housing 301 flows the central portion in the lengthwise direction within the housing 301. Consequently, the areas S residing near the ends of the bundle 304 of the hollow fiber membranes do not contribute to the exchange of water in a sufficient manner and, thus there is a problem that the ratio of moisture recovery at such portions unduly low in relative to the permeable water within the hollow fiber membranes.
The first object of the present invention is to make it possible to water exchange in a sufficient manner even at the portions near the ends of the hollow fiber membranes of the bundle of the hollow fiber membranes stored within the housing to thereby improve the ratio of moisture recovery of the humidifier.
The second object of the present invention is to provide a humidifier which can improve the recovery of water utilizing a turbulent flow when the dry air flows outside a bundle of hollow fiber membranes composed of a plurality of water-permeable hollow fiber membranes accommodated within the housing of the hollow fiber membrane module.
The third object of the present invention is to provide a humidifier suitably used for the humidification of the fuel cell, which can improve the water-permeability from the moist gas to the dry gas.
(First Aspect)
According to the first of the present invention which can attain these and other objects, there is provided a humidifier having a plurality of water-permeable hollow fiber membranes placed along the lengthwise direction of a housing accommodated within the housing in which gases each having a different moisture content flow inside and outside said hollow fiber membranes to carry out moisture exchange whereby the dry air having a low moisture content is humidified, said humidifier comprising a gas inlet which introduce the gas flowing outside the hollow fiber membranes within the housing formed on an end of the lengthwise direction of the housing.
According to the first aspect of the present invention, a gas inlet which introduce the gas flowing outside the hollow fiber membranes within the housing is formed on an end of the lengthwise direction of the housing. For this reason, the gas flowing outside of the hollow fiber membranes can be spread over the ends of the housing and, thus the water exchange can be carried out in a sufficient manner, even at the ends of the bundle of the hollow fiber membranes.
In the humidifier according to the first aspect, an injector which injects the gas flowing outside the hollow fiber membranes may be placed directionally to an end of the lengthwise direction of the housing.
In this embodiment, the gas flowing outside the hollow fiber membranes is injected toward the end of the housing. For this reason, the gas flowing outside of the hollow fiber membranes can be spread over the ends of the housing. Consequently, the water exchange can be carried out in much more sufficient manner, not only at the center but also at the ends of the bundle of the hollow fiber membranes, improving the recovery of water.
In the humidifier according to the first aspect, an injector which injects the gas flowing outside the hollow fiber membranes may also be placed toward the center of the lengthwise direction of the housing, alternative to the direction of the end of the housing.
In this embodiment, the gas flowing outside the hollow fiber membranes is injected from the end(s) of the lengthwise direction of the housing toward the center of the housing. Due to the current of the gas flowing outside the hollow fiber membranes, the gas flowing outside the hollow fiber membranes can be supplied over the whole areas of the housing. As a result, the water can be effectively recovered from the entire areas of bundle of the hollow fiber membranes including the ends of the housing, improving the recovery of the water.
In the humidifier according to the first aspect where the injector is provided, a generator which generate a circular flow of the gas flowing outside the hollow fiber membranes injected from the injector may be provided.
According to this embodiment, the gas flowing outside the hollow fiber membranes is injected as a circular flow. This makes the gas flowing outside the hollow fiber membranes turbulent flow. Due to the turbulent flow of the gas flowing outside the hollow fiber membranes, the gas flowing outside the hollow fiber membranes can be spread over the entire area of the housing from one end to another end of the housing in much more effective manner. What is more, the gas flowing outside the hollow fiber membranes can reside within the housing over a prolonged period of time, which contributes to the improvement in the recovery of water.
The humidifier according to the first aspect of the present invention can be suitably used as the humidifier in a fuel cell system.
According to the first aspect of the present invention, there is also provided a humidification process utilizing a hollow fiber membrane module comprising a plurality of water-permeable hollow fiber membranes placed along the lengthwise direction of a housing accommodated within the housing, in which gases each having a different moisture content flow inside and outside said hollow fiber membranes to carry out moisture exchange whereby the dry air having a low moisture content is humidified, said process comprising injecting the gas flowing outside the hollow fiber membranes toward an end or the center of the lengthwise direction of the housing.
According such a configuration, the gas flowing outside of the hollow fiber membranes can be spread over the ends of the housing and, thus the water exchange can be carried out in a sufficient manner, even at the ends of the bundle of the hollow fiber membranes. Alternatively due to the current of the gas flowing outside the hollow fiber membranes, the gas flowing outside the hollow fiber membranes can be supplied over the whole areas of the housing. As a result, the water can be effectively recovered from the entire areas of bundle of the hollow fiber membranes including the ends of the housing, improving the recovery of the water.
(Second Aspect)
According to the second aspect of the present invention which can attain these and other objects, there is provided a humidifier having a plurality of water-permeable hollow fiber membranes placed along the lengthwise direction of a housing accommodated within the housing in which gases each having a different moisture content flow inside and outside said hollow fiber membranes to carry out moisture exchange whereby the dry air having a low moisture content is humidified, said humidifier having a construction for generating a turbulent flow provided on the inner surface of said housing.
By providing the construction for generating a turbulent flow on the inner surface of the housing, since the dry gas rectified along the inner surface to be laminar flow collides with the construction for generating a turbulent flow to be a turbulent flow, the dry air thoroughly flows over the external surface of the bundle of hollow fiber membranes. Accordingly, the moisture recovery (humidified amount) becomes large where the dry gas having a low moisture content recovers the moisture (water) from the moist gas having a large moisture content.
In this humidifier according to the second aspect, the construction for generating a turbulent flow is a groove or grooves provided on the inner surface of the housing.
By providing the grooves on the inner surface of the housing, the dry gas rectified along the inner surface to be laminar flow may be disturbed at the grooves to be a turbulent flow. As a result, the dry gas uniformly flows on the external surface of the bundle of the hollow fiber membranes accommodated within the housing and thus, the moisture recovery (humidified amount) becomes large where the dry gas having a low moisture content recovers the moisture (water) from the moist gas having a large moisture content.
In this humidifier according to the second aspect, the construction for generating a turbulent flow is a projection or projections provided on the inner surface of the housing.
By providing the projections on the inner surface of the housing, the dry gas rectified along the inner surface to be laminar flow may be disturbed at the grooves to be a turbulent flow. As a result, the dry gas uniformly flows on the external surface of the bundle of the hollow fiber membranes accommodated within the housing and thus, the moisture recovery (humidified amount) becomes large where the dry gas having a low moisture content recovers the moisture (water) from the moist gas having a large moisture content.
In this humidifier according to the second aspect, the construction for generating a turbulent flow is made up of the housing swelled symmetrically with the axis.
Due to the housing swelled symmetrically with the axis, the flow of the dry gas within the housing can be a circular flow along the circumference and, thus, the dry gas can flow from the outside to the central side of the bundle of the hollow fiber membranes accommodated within the housing. Accordingly, the dry gas collides with the bundle of the hollow fiber membranes and disturbed to be a turbulent flow. As a result, the dry gas uniformly flows on the external surface of the bundle of the hollow fiber membranes accommodated within the housing and thus, the moisture recovery (humidified amount) becomes large where the dry gas having a low moisture content recovers the moisture (water) from the moist gas having a large moisture content.
The humidifier according to the second aspect of the present invention can be suitably used as the humidifier in a fuel cell system.
According to the second aspect of the present invention, there is also provided a humidification process utilizing a hollow fiber membrane module comprising a plurality of water-permeable hollow fiber membranes placed along the lengthwise direction of a housing accommodated within the housing, in which gases each having a different moisture content flow inside and outside said hollow fiber membranes to carry out moisture exchange whereby the dry air having a low moisture content is humidified, said process comprising generating a turbulent flow of the gas flowing outside said hollow fiber membranes within the inner surface of the housing.
By generating a turbulent flow of the gas flowing outside said hollow fiber membranes within the inner surface of the housing, since the dry gas rectified along the inner surface to be laminar flow collides with the construction for generating a turbulent flow to be a turbulent flow, the dry air thoroughly flows over the external surface of the bundle of hollow fiber membranes. Accordingly, the moisture recovery (humidified amount) becomes large where the dry gas having a low moisture content recovers the moisture (water) from the moist gas having a large moisture content.
(Third Aspect)
According to the third aspect of the present invention which can attain these and other objects, there is provided a humidifier having a plurality of water-permeable hollow fiber membranes placed along the lengthwise direction of a housing accommodated within the housing in which gases each having a different moisture content flow inside and outside said hollow fiber membranes to carry out moisture exchange whereby the dry air having a low moisture content is humidified, said humidifier having a construction for generating a turbulent flow provided within the hollow fiber membranes.
By providing the construction for generating a turbulent current within the hollow fiber membranes, the gas whose moisture distribution is uniform flows within the inner surface of the hollow fiber membrane. Consequently, in comparison with the laminar flow, the difference in the moisture contents between the gas inside the hollow fiber membrane and the gas flowing outside the hollow fiber membrane near the gas inside the hollow fiber membrane can take a large. Accordingly, the water-permeability from the moist gas to the dry gas can be enhanced. Either the moist gas or the dry gas may flow inside the hollow fiber membrane. In any case, the gas flows as a turbulent flow to enhance the water-permeability. In the following embodiments, the humidifier in which the off gas, which is a moist gas in the fuel cell flows inside the hollow fiber membrane is exemplified.
In this humidifier according to the third aspect, the construction for generating a turbulent flow is projections provided on the inner surface of the hollow fiber membrane.
By providing the projection(s) on the inner surface of the hollow fiber membrane, the gas can be collided with the projection(s) to form a turbulent flow As a result, the gas having a uniform moisture distribution flows inside of the hollow fiber membrane and thus, the water-permeability from the moist gas to the dry gas can be enhanced.
In this humidifier according to the third aspect, the construction for generating a turbulent flow is a twisted fin provided at an inlet portion for introducing the gas into the interior of the hollow fiber membrane.
By providing a twisted fin at an inlet portion for introducing the gas into the interior of the hollow fiber membrane and stirring the gas flowing inside the hollow fiber membrane, the gas flows as a turbulent flow. As a result, the gas having a uniform moisture distribution flows inside of the hollow fiber membrane and thus, the water-permeability from the moist gas to the dry gas can be enhanced.
In this humidifier according to the third aspect, the construction for generating a turbulent flow is a step provided at an inlet portion for introducing the gas into the interior of the hollow fiber membrane.
By providing a step at an inlet portion for introducing the gas into the interior of the hollow fiber membrane and stirring the gas flowing inside the hollow fiber membrane, the gas flows as a turbulent flow. As a result, the gas having a uniform moisture distribution flows inside of the hollow fiber membrane and thus, the water-permeability from the moist gas to the dry gas can be enhanced.
The humidifier according to the third aspect of the present invention can be suitably used as the humidifier in a fuel cell system.
According to the third aspect of the present invention, there is provided a humidification process utilizing a hollow fiber membrane module comprising a plurality of water-permeable hollow fiber membranes placed along the lengthwise direction of a housing accommodated within the housing, in which gases each having a different moisture content flow inside and outside said hollow fiber membranes to carry out moisture exchange whereby the dry air having a low moisture content is humidified, said process comprising generating a turbulent flow of the gas flowing inside said hollow fiber membranes within said hollow fiber membranes.
By generating a turbulent flow of the gas flowing inside said hollow fiber membranes within said hollow fiber membranes, the gas whose moisture distribution is uniform flows within the inner surface of the hollow fiber membrane. Consequently, in comparison with the laminar flow, the difference in the moisture contents between the gas inside the hollow fiber membrane and the gas flowing outside the hollow fiber membrane near the gas inside the hollow fiber membrane can take a large. Accordingly, the water-permeability from the moist gas to the dry gas can be enhanced. Either the moist gas or the dry gas may flow inside the hollow fiber membrane. In any case, the gas flows as a turbulent flow to enhance the water-permeability. In the following embodiments, the humidifier in which the off gas, which is a moist gas in the fuel cell flows inside the hollow fiber membrane is exemplified.